如何为 Iterator<Item = String> 实现 std::io::Read？

Question

更具体地说，我正在采用标准，过滤掉某些行，.lines().filter_map()并且我想将其结果与csv::Reader.

Answer 1

标准库提供了std::io::Cursor将缓冲区与缓冲区中的位置包装在一起的类型。这可以用来进一步简化Veedrac 的答案中给出的代码：

use std::io::{self, Cursor, Read};

struct IteratorAsRead<I>
where
    I: Iterator,
{
    iter: I,
    cursor: Option<Cursor<I::Item>>,
}

impl<I> IteratorAsRead<I>
where
    I: Iterator,
{
    pub fn new<T>(iter: T) -> Self
    where
        T: IntoIterator<IntoIter = I, Item = I::Item>,
    {
        let mut iter = iter.into_iter();
        let cursor = iter.next().map(Cursor::new);
        IteratorAsRead { iter, cursor }
    }
}

impl<I> Read for IteratorAsRead<I>
where
    I: Iterator,
    Cursor<I::Item>: Read,
{
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        while let Some(ref mut cursor) = self.cursor {
            let read = cursor.read(buf)?;
            if read > 0 {
                return Ok(read);
            }
            self.cursor = self.iter.next().map(Cursor::new);
        }
        Ok(0)
    }
}

#[test]
fn small_pieces_are_combined() {
    let iterable = ["h", "e", "l", "l", "o"];
    let mut reader = IteratorAsRead::new(&iterable);

    let mut buf = vec![];
    let bytes = reader.read_to_end(&mut buf).unwrap();
    assert_eq!(&buf[..bytes], b"hello");
}

#[test]
fn partial_reads() {
    let iterable = ["hello"];
    let mut reader = IteratorAsRead::new(&iterable);

    let mut buf = [0; 2];

    let bytes = reader.read(&mut buf).unwrap();
    assert_eq!(&buf[..bytes], b"he");

    let bytes = reader.read(&mut buf).unwrap();
    assert_eq!(&buf[..bytes], b"ll");

    let bytes = reader.read(&mut buf).unwrap();
    assert_eq!(&buf[..bytes], b"o");
}

操场